Wax seals have been used since antiquity to guarantee the integrity and authenticity of documents The traditional bee-wax or tallow-wax seal is formed by applying a glob of melted wax on a document, ribbon or fastener, then stamping the melted glob with a brass seal engraved with a mirror image of the desired design.
Nowadays, this type of wax seal is seldom used to certify a document, but survives only as a decorative element that lends class and distinction to a diploma, award certificate, or personal missive.
Traditional wax seals are very brittle, and cannot survive the sorting and canceling machines used in most post offices Their debris can interfere with the good operation of that type of equipment. Accordingly, envelopes bearing a natural wax seal must be hand-delivered to a post office where they are manually canceled and sorted.
Brass seals are relatively expensive. Moreover, the whole process of melting the wax, applying a glob of it to the document, then stamping it is awkward for most people and is often botched.